60
260
Upstream Edge
of Freezeup Jam
40
250
Figure 8. Temporal variation of
Daily Mean
20
Air Temperature
air temperature and location of
upstream edge of a freezeup jam
0
240
on the Salmon River, Idaho,
199091.
20
230
0
40
80
120
160
Julian Day (1 Oct = 1)
Factor of the Hudson's Bay Co. post at Fort McMurray in Alberta and described the
following events on the morning of 20 April 1875:
...The winter of 187475 was a bitter one, with deep snow and never a thaw until
April. On the 2nd or 3rd of that month, however, a further heavy fall of snow was
followed by a sudden rise in temperature. The change of weather and the weight of
melting snow caused the ice for the 85 mile stretch of rapids above the fort [Fort
McMurray] to breakup, and it came down the Athabasca with terrific force. On strik-
ing the turn of the stream at the post it blocked the river and drove the ice 2 miles up
the Clearwater [a major tributary] in piles 40 to 50 feet high. In less than an hour the